Writing instrument cap



FIG. 1 is a right front perspective view of a writing instrument cap showing our new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a right side elevational view, the left side being a mirror image thereof;

FIG. 4 is a bottom plan view thereof; and

FIG. 5 is a top plan view thereof. 

The ornamental design for a writing instrument cap, as shown and described. 